This invention relates to an anti-reflective coating composition and, more particularly, to an anti-reflective coating composition which prevents reflection of incident light and substrate-reflected light at the surface of a resist upon formation of a pattern by photolithography technique, and to a method of forming a pattern using this anti-reflective coating composition.
In the field of manufacturing semiconductor elements, there has been applied lithography technique in which a photoresist coating is formed on a substrate such as silicon wafer and, after selectively exposing this with actinic rays, development processing is conducted to form a resist pattern on the substrate.
In recent years, miniaturization of processing size in the lithography process has rapidly been developed for attaining higher integration degree in the field of LSI. In the miniaturization of processing size, there have been made various proposals in all respects such as an exposing apparatus, a photoresist, an anti-reflective coating, etc.
Use of short and single wavelength radiation upon exposure such as in an i-line exposure process at present being widely used causes mutual interference of incident light, reflected light from the photoresist/substrate interface and re-reflected light of this reflected light at the photoresist/air interface within the photoresist layer. The mutual interference causes a problem of standing wave or phenomenon of multiple reflection due to change of substantial exposure amount within the photoresist layer to adversely affect form of a formed resist pattern. As the result, in a line pattern-forming process, there can result insufficient uniformity of line width of a resist pattern or, in a process of forming contact holes on a stepped substrate, there can result opening failure due to difference in substantial optimal sensitivity since the resist layer is not uniform in thickness.
In order to solve the problem described above, a process has conventionally been proposed in which an anti-reflective coating is formed on a photoresist layer, and various anti-reflective coating compositions for use in this anti-reflective coating have also been proposed. For example, Japanese Unexamined Patent Publication No. H05-188598, an anti-reflective coating composition containing a water-soluble polymer binder and a functional fluorocarbon compound to be coated on a photoresist layer is disclosed. In these processes wherein photoresist for i-line and an anti-reflective coating are used, resulting resist patterns sometimes form T-top to some extent depending upon formulation of the photoresist, temperature of heating treatment, etc., which is becoming a problem.
On the other hand, there have been proposed and partly being put into practice processes of using a short wavelength radiation source effective for forming a much finer pattern, such as a process of using deep-UV rays such as KrF excimer laser (248 nm), ArF excimer laser (193 nm) or the like or even X-rays or electron beams as the exposure radiation source. In the process of using these short wavelength radiation sources, chemically amplified resists are proposed as preferable photoresists.
In the case of using such chemically amplified resist as the photoresist, an anti-reflective coating composition proposed, for example, in the above-mentioned Japanese Unexamined Patent Publication No. H05-188598 tends to cause intermixture of the components in the anti-reflective coating composition and the photoresist, which results in formation of T-top with positive-working resists or formation of round top with negative-working resists. Japanese Unexamined Patent Publication No. H06-69120 discloses to coat an anti-reflective coating composition having been adjusted to alkaline on a resist containing a novolak resin and a naphthoquinonediazide compound, to thereby cause crosslinking reaction in the photoresist layer with the alkali contained in the anti-reflective coating composition being a catalyst. As the result, surface of the photoresist layer is made so slightly soluble that there can be obtained a good pattern suffering less loss of the layer. However, this process involves a problem that it can be applied only to a positive-working resist containing novolak resin and naphthoquinonediazide.
In view of these circumstances, an object of the present invention is to provide an anti-reflective coating composition which does not cause the above-described problems with conventional anti-reflective coating compositions, that is, which never suffers deterioration of pattern form, particularly formation of T-top with chemically amplified positive-working resists or formation of round top with negative-working resists, to be caused by intermixing of the components of the composition and the photoresist.
Another object of the present invention is to provide a method for forming a resist pattern which enables one to form a resist pattern with excellent profile even when an anti-reflective coating is formed by coating on a photoresist layer.
As a result of intensive investigations, the inventors have found that the above-described objects can be attained by using, as an anti-reflective coating composition to be coated on a photoresist layer, a composition which comprises at least the following (a), (b), (c) and (d), thus having achieved the present invention based on the finding.
That is, the present invention relates to an anti-reflective coating composition which comprises at least the following (a), (b), (c) and (d):
(a) polyacrylic acid;
(b) polyvinyl pyrrolidone;
(c) CnF2n+1COOH (wherein n represents an integer of 3 to 11); and
(d) tetramethylammonium hydroxide.
The present invention also relates to a method for forming a resist pattern, which comprises coating the above-described anti-reflective coating composition onto a photoresist layer.
The present invention is now described in more detail below.
Firstly, water-soluble resin of polyacrylic acid to be used in the present invention as component (a) preferably has a molecular weight of 1,000 to 4,000,000 as determined by polystyrene standards, and water-soluble resin of polyvinyl pyrrolidone to be used as component (b) preferably 1,000 to 360,000. Ratio of acrylic acid (a) to polyvinyl pyrrolidone (b), i.e., (a):(b) is preferably 99.5:0.5 to 50:50 (by weight; hereinafter the same unless otherwise specified), more preferably 95:5 to 88:12. The polyacrylic acid component and the polyvinyl pyrrolidone component may be previously mixed, if necessary, to be used as a mixture.
Secondly, perfluoroalkylcarboxylic acid to be used in the present invention as component (c) may be any of those that contain 3 to 11 carbon atoms in the perfluoroalkyl group. They may be used independently or as a mixture of two or more of them. As the perfluoroalkylcarboxylic acid to be used in the present invention, perfluoro-octanoic acid is particularly preferred.
Further, in the anti-reflective coating composition of the present invention, proportion of the water-soluble resins of polyacrylic acid (a) and polyvinyl pyrrolidone (b), perfluoroalkylcarboxylic acid (c) and tetramethylammonium hydroxide, i.e., [(a)+(b)]:(c):(d), is preferablyl 1.0:1.0xe2x88x927.0:0.1xe2x88x921.0.
Various additives may optionally be compounded in the anti-reflective coating composition of the present invention within the range of not damaging the properties of the composition. As one of such additives, there is a surfactant to be added for the purpose of improving coating properties or the like. Specific examples of the surfactant include nonionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene lauryl ether, polyoxyethylene oleyl ether, polyoxyethylene cetyl ether, polyoxyethylene fatty acid diester, polyoxyethylene fatty acid monoester, polyoxyethylene polyoxypropylene block polymer, acetylene glycol and the derivatives thereof, etc.; anionic surfactants such as alkyldiphenyl ether disulfonic acid and the ammonium or organic amine salts thereof, alkyldiphenyl ether sulfonic acid and the ammonium or organic amine salt thereof, alkylbenzenesulfonic acid and the ammonium or organic amine salt thereof, polyoxyethylene alkyl ether sulfulic acid and the ammonium or organic amine salt thereof, alkylsufulic acid and the ammonium or organic amine salt thereof, etc.; and amphoteric surfactants such as 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine, lauric acid amide propylhydroxysulfon betaine, etc.
The components of the anti-reflective coating composition of the present invention are dissolved in water to prepare the anti-reflective coating composition. Water to be used in the anti-reflective coating composition of the present invention is not particularly limited as long as it is water, but water from which organic impurities, metallic ions, etc. have been removed by distillation, ion-exchange treatment, filter treatment, various adsorption treatment, etc. is preferred.
Additionally, in the anti-reflective coating composition of the present invention may be used a water-soluble organic solvent together with water in order to improve coating properties. As such water-soluble organic solvent, any solvent that is soluble in water may be used with no particular limits, and examples thereof include alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, etc.; ketones such as acetone, methyl ethyl ketone, etc.; esters such as methyl acetate, ethyl acetate, etc.; and polar solvents such as dimethylformamide, dimethylsulfoxide, methylcellosolve, cellosolve, butylcellosolve, cellosolve acetate, butylcarbitol, carbitol acetate, etc. These specific examples are illustrated as mere examples of the organic solvents and should not be construed to limit the organic solvents that can be used in the present invention.
The anti-reflective coating composition of the present invention is coated on a photoresist layer by a conventionally known method such as spin coating. Refractive index (na) of the anti-reflective coating formed by such coating method is preferably a square root of the refractive index of the resist layer (nr), and thickness of the anti-reflective coating is preferably an odd number of times as much as the value of xcexe/4na wherein xcexe represents wavelength of the exposing radiation. In the present invention, the anti-reflective coating is formed on the resist layer by using the above-described anti-reflective coating composition, and then exposure and development are conducted in the conventional manner to form a resist pattern. As the photoresist to which the anti-reflective coating composition of the present invention is applied, any of those that have conventionally been known may be used, with chemically amplified resists being preferable.
The present invention will now be described more specifically by reference to Examples which, however, are not to be construed to limit the present invention in any way.